Compressor driving torque estimating apparatus and compressor driving source control apparatus

ABSTRACT

A compressor driving torque estimating apparatus estimates driving torque of a compressor. The apparatus includes a discharge-side detecting device, an inlet-side detecting device, first and second calculating devices, and an estimated driving torque determining device. The discharge-side detecting device detects discharge-side quantity about fluid discharged from the compressor. The inlet-side detecting device detects inlet-side quantity about fluid drawn into the compressor. The first calculating device calculates first estimated driving torque based on the discharge- and inlet-side quantity. The second calculating device calculates second estimated driving torque based on the discharge-side quantity. The estimated driving torque determining device chooses a smaller value between the first and second estimated driving torque as the driving torque. A compressor driving source control apparatus includes the apparatus. The control apparatus controls an output of a driving source, which provides driving force for the compressor, based on the driving torque.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2006-107162 filed on Apr. 10, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a compressor driving torque estimating apparatus and a compressor driving source control apparatus.

2. Description of Related Art

A variable displacement compressor, which obtains driving force from a vehicle engine, is conventionally employed as a refrigerant compressor of an air conditioner for a vehicle. In such a vehicle, generally by estimating driving torque of the compressor and controlling an engine output based on the estimated driving torque, an engine rotational speed does not change even if the driving torque of the compressor varies.

In JP2001-180261A (corresponding to U.S. Pat. No. 6,336,335B2, US2001008131 A1), for example, the driving torque of the compressor is estimated based on a control signal that electrically controls a discharge volume changing mechanism of the variable displacement compressor externally, and output torque of the engine is controlled in such a manner that the estimated driving torque is added.

However, in operating the discharge volume changing mechanism of the variable displacement compressor, a mechanical operational delay (response lag) is caused in response to a change in the control signal. Accordingly, as in JP2001-180261A, when the driving torque is estimated based on the control signal, a great difference between the estimated driving torque and actual driving torque arises in a transient state, in which discharge volume changes considerably (e.g., immediately after the variable displacement compressor starts compression).

In JP2006-105030A (corresponding to US2006/0073047A1), the present applicant proposes a compressor driving torque estimation method, whereby smaller driving torque is chosen between first estimated driving torque and second estimated driving torque as the estimated driving torque. The first estimated driving torque is calculated such that it gradually increases according to a time that elapses after the compressor compresses refrigerant. The second estimated driving torque is calculated based on a compressor discharge refrigerant pressure.

According to the estimation method in JP2006-105030A, the first estimated driving torque is calculated such that it is smaller than the second estimated driving torque in the transient state immediately after the compressor starts compression. Consequently, the first estimated driving torque that gradually increases according to the elapsed time is adopted as the estimated driving torque. As a result, the great difference between the estimated driving torque and the actual driving torque in the transient state is limited.

The first estimated driving torque can be calculated based on the volume control signal in JP2006-105030A. However, according to the present inventor's further examination, even though the first estimated driving torque is calculated based on the volume control signal, the difference between the estimated driving torque and the actual driving torque cannot be completely prevented.

SUMMARY OF THE INVENTION

The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to limit a difference between estimated driving torque and actual compressor driving torque in a transient state immediately after a variable displacement compressor starts compression.

To achieve the objective of the present invention, there is provided a compressor driving torque estimating apparatus for estimating driving torque of a variable displacement compressor, discharge volume of fluid of which is variable. The apparatus includes a discharge side detecting means, an inlet side detecting means, a first estimated driving torque calculating means, a second estimated driving torque calculating means, and an estimated driving torque determining means. The discharge side detecting means is for detecting discharge side physical quantity about fluid discharged from the variable displacement compressor. The inlet side detecting means is for detecting inlet side physical quantity about fluid drawn into the variable displacement compressor. The first estimated driving torque calculating means is for calculating first estimated driving torque of the variable displacement compressor based on the discharge side physical quantity and the inlet side physical quantity. The second estimated driving torque calculating means is for calculating second estimated driving torque of the variable displacement compressor based on the discharge side physical quantity. The estimated driving torque determining means is for choosing a smaller value between the first estimated driving torque and the second estimated driving torque as the driving torque.

To achieve the objective of the present invention, there is also provided a compressor driving source control apparatus including the compressor driving torque estimating apparatus. The compressor driving source control apparatus controls an output of a driving source, which provides driving force for the variable displacement compressor, based on the driving torque estimated by the compressor driving torque estimating apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is an overall configuration diagram of an idle-speed control apparatus according to a first embodiment of the present invention;

FIG. 2 is a flowchart showing control of the idle-speed control apparatus according to the first embodiment;

FIG. 3 is a flowchart showing a chief part of the control of the idle-speed control apparatus according to the first embodiment;

FIG. 4 is an illustrative graph showing a relationship between estimated driving torque and actual driving torque according to the first embodiment;

FIG. 5 is a graph showing a relationship between a discharge refrigerant pressure and a control current; and

FIG. 6 is an illustrative graph showing variation of the actual driving torque.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is devised based on the following experimental knowledge. In a variable displacement compressor having the same configuration as a first embodiment (described later), the present inventor examines variation of actual driving torque immediately after the compressor starts compression. FIG. 6 is a graph showing results of the examination, with its horizontal axis being an elapsed time T, and its vertical axis being the actual driving torque of the compressor.

The results of the examination, in which a discharge refrigerant pressure (Pd) and a suction refrigerant pressure (Ps) at the time the compressor starts compression are varied according to three conditions, are plotted on the graph in FIG. 6. More specifically, the three conditions include a condition 1 (C1: indicated by continuous line) of Pd=3.0 Mpa and Ps=0.5 Mpa, a condition 2 (C2: indicated by dashed-two dotted line) of Pd=3.0 Mpa and Ps=0.2 Mpa, and a condition 3 (C3: indicated by dashed line) of Pd=1.5 Mpa and Ps=0.2 Mpa.

In comparison between C1 and C2 in FIG. 6, when the suction refrigerant pressure (Ps) is high, a response time (Tn) from the time a variable displacement compressor (10) starts compression until the actual driving torque of the compressor starts increasing becomes short, even though the discharge refrigerant pressure (Pd) is the same. Furthermore, as can be seen from FIG. 6, an increase rate (ΔTrk) of the torque per unit time after the response time (Tn) elapses increases.

Moreover, in comparison between C2 and C3, when the discharge refrigerant pressure (Pd) is high, the response time (Tn) becomes long, and the increase rate (ΔTrk) of the torque decreases even though the suction refrigerant pressure (Ps) is the same.

That is, the response time (Tn) and the increase rate (ΔTrk) of the torque in a transient state vary according to the discharge refrigerant pressure (Pd) and the suction refrigerant pressure (Ps) at the time the compressor starts compression. Consequently, by estimating driving torque of a compressor in the transient state based on the discharge refrigerant pressure (Pd) and the suction refrigerant pressure (Ps), an accurate estimate can be made with its difference from the actual driving torque being restricted.

Furthermore, according to the results of the experiments above, when a high-low pressure ratio (Pd/Ps) between the discharge refrigerant pressure (Pd) and the suction refrigerant pressure (Ps) at the time the compressor starts compression is small, the response time (Tn) becomes short, and the increase rate (ΔTrk) of the torque increases. In FIG. 6, the response times (Tn) under the conditions 1 to 3 are indicated by T1 to T3, respectively.

In addition, symbols and numerals that appear above in parentheses correspond to concrete measures described in the following embodiments.

First Embodiment

A first embodiment of the present invention is described with reference to FIGS. 1 to 4. According to the first embodiment, the present invention is applied to an idle-speed control apparatus for a vehicle. The vehicle of the first embodiment employs a variable displacement compressor 10, which obtains driving force from an engine for vehicle traveling as a refrigerant compressor of a vehicle air conditioner. The idle-speed control apparatus controls an engine rotational speed based on estimated driving torque STrk (described later) of the variable displacement compressor 10.

FIG. 1 is an overall configuration diagram of the idle-speed control apparatus of the first embodiment. An engine (not shown) has an inlet pipe 20, in which a throttle valve 20 a is placed. The throttle valve 20 a regulates an amount of intake air into the inlet pipe 20 according to a degree of opening when an accelerator pedal of the vehicle is depressed. In the engine, the engine rotational speed (output power) is regulated according to the intake air amount and injection quantity.

The inlet pipe 20 has a by-pass line 20 b, and an idle adjusting valve 20 c is placed in the by-pass line 20 b. The idle adjusting valve 20 c changes a bypassed amount of an intake airflow from an upstream side to a downstream side of the throttle valve 20 a according to the degree of valve opening. An idle speed of the engine is regulated by the bypassed amount of the intake airflow.

The idle adjusting valve 20 c includes a known linear solenoid valve, and is electrically controlled by a driving voltage Visc outputted from an electrical control unit (described later) to change its degree of opening.

A refrigerating cycle Rc, which is included in the vehicle air conditioner, is disposed in an engine room, and includes the variable displacement compressor 10. In the refrigerating cycle Rc, the variable displacement compressor 10 draws refrigerant on a downstream side of an evaporator 70 (described later) via a piping P1 to be compressed and discharged. The variable displacement compressor 10 is driven to rotate when the driving force is transmitted from the engine via a magnetic clutch 30 and a belt mechanism (not shown).

Thus, in the first embodiment, a driving source, which provides the driving force to the variable displacement compressor 10, is the engine. A known skew-plate variable displacement compressor, which continuously takes variable control over its discharge volume through an external control signal, is employed as the variable displacement compressor 10. Additionally, the discharge volume is geometric volume of a working space, in which refrigerant is drawn and compressed, and more specifically, cylinder volume between a top dead center and a bottom dead center of a piston stroke.

Accordingly, by changing the discharge volume, a discharge capacity of the variable displacement compressor 10 is regulated. The discharge volume is changed by controlling a pressure Pc of a skew plate room (not shown) in the variable displacement compressor 10 to change an inclination angle of a skew plate and change the piston stroke.

The pressure Pc of the skew plate room is controlled by changing a rate between a discharge refrigerant pressure Pd and a suction refrigerant pressure Ps, which are led to the skew plate room, using an electromagnetic volume control valve 10 a that is controlled by the control signal (control current: In) outputted from a microcomputer 100 of the electrical control unit (described later). As a result, the variable displacement compressor 10 continuously changes the discharge volume in a range of approximately 0% to 100%.

In addition, since the variable displacement compressor 10 continuously changes the discharge volume in the range of approximately 0% to 100%, an operation of the variable displacement compressor 10 can be substantially stopped by decreasing the discharge volume to around 0%. Thus, a clutchless configuration, in which a rotational axis of the variable displacement compressor 10 is constantly coupled to the engine of the vehicle via the belt mechanism, may be employed.

An outlet side of the variable displacement compressor 10 is connected to an inlet side of a condenser 40 via a piping P2. The condenser 40 is arranged between the engine and a front grille (not shown) of the vehicle in the engine room. The condenser 40 is a radiator that cools refrigerant by exchanging heat between refrigerant discharged from the variable displacement compressor 10 and outer air blown by a fan 40 a.

An outlet side of the condenser 40 is connected to an inlet side of a vapor-liquid separator 50 via a piping P3. The vapor-liquid separator 50 separates refrigerant cooled in the condenser 40 into a vapor phase and a liquid phase. A liquid-phase refrigerant outlet side of the vapor-liquid separator 50 is connected to an expansion valve 60 via a piping P4. The expansion valve 60 decompresses and expands liquid-phase refrigerant separated in the vapor-liquid separator 50, and regulates a flow rate of refrigerant that flows out of an outlet side of the expansion valve 60.

More specifically, the expansion valve 60 has a temperature sensitive tube 60 a that detects temperature of refrigerant in the piping P1. The expansion valve 60 detects a degree of superheat of refrigerant on an inlet side of the variable displacement compressor 10 based on temperature and pressure of refrigerant drawn to the variable displacement compressor 10 (i.e., refrigerant in the piping P1), and regulates its degree of opening such that the degree of superheat coincides with a predetermined value.

A downstream side of the expansion valve 60 is connected to the evaporator 70 via a piping P5. The evaporator 70 exchanges heat between refrigerant decompressed and expanded by the expansion valve 60 and air blown by a fan 70 a. The evaporator 70 is a heat exchanger, in which low-pressure refrigerant flown into the evaporator 70 absorbs heat from the blown air to evaporate, and thereby the blown air is cooled down.

The downstream side of the evaporator 70 is connected to the piping P1. Refrigerant evaporated flows into the variable displacement compressor 10 again. In this manner, refrigerant circulates around the refrigerating cycle Rc, which includes the variable displacement compressor 10, the condenser 40, the vapor-liquid separator 50, the expansion valve 60, the evaporator 70, and the variable displacement compressor 10 in this order.

A general description of the electrical control unit of the first embodiment is given. The electrical control unit includes the known microcomputer 100 including a CPU, an ROM, an RAM, and the like and its peripheral circuits 110, 131 to 133. The microcomputer 100 stores a control program for the air-conditioning controllers 10 a, 30, 70 a and the idle adjusting valve 20 c in the ROM. The microcomputer 100 performs various operations and processing based on the control program.

Sensor detection signals are inputted into the microcomputer 100 from a group of air-conditioning sensors 121 to 125 via an A/D converter 110, which is the peripheral circuit. As well, operation signals from various air-conditioning operation switches SW on an air-conditioning operation panel disposed near an instrument panel at a front part of a vehicle compartment and a detection signal of an engine tachometer 126, which detects the engine rotational speed Ne, are inputted into the microcomputer 100.

More specifically, the group of air-conditioning sensors 121 to 125 are an outside air sensor 121, an inside air sensor 122, a solar radiation sensor 123, an evaporator temperature sensor 124, and a high-pressure pressure sensor 125. The outside air sensor 121 detects an outside air temperature Tam. The inside air sensor 122 detects an inside air temperature Tr. The solar radiation sensor 123 detects a solar radiation amount Ts, which is incoming into the vehicle compartment. The evaporator temperature sensor 124 is disposed at an air outlet part of the evaporator 70 and detects an evaporator outlet air temperature Te. The high-pressure pressure sensor 125 detects the discharge refrigerant pressure Pd of refrigerant discharged from the variable displacement compressor 10.

In the first embodiment, the high-pressure pressure sensor 125 is “a discharge side detecting means” for detecting physical quantity about a discharge pressure of the variable displacement compressor 10, and the discharge refrigerant pressure Pd is a discharge side detection value. The high-pressure pressure sensor 125 is provided generally to sense an abnormal pressure in the refrigerating cycle Rc, and there is no need to newly provide “a dedicated detecting means” for detecting the physical quantity about the discharge pressure.

Furthermore, in the first embodiment, the evaporator temperature sensor 124 is “an inlet side detecting means” for detecting physical quantity about an inlet pressure of the variable displacement compressor 10, and the evaporator outlet air temperature Te is an inlet side detection value. Since the evaporator outlet air temperature Te is approximately the same as a refrigerant evaporation temperature in the evaporator 70, a refrigerant evaporation pressure in the evaporator 70 (i.e., an inlet pressure of the variable displacement compressor 10) can be determined by the refrigerant evaporation temperature.

The various air-conditioning operation switches SW on the air-conditioning operation panel include an air-conditioning switch, an outlet mode switch, an automatic switch, and a temperature setting switch. The air-conditioning switch gives a command signal to actuate the variable displacement compressor 10. The outlet mode switch sets an outlet mode. The automatic switch gives a command signal for an air-conditioning automatic control state. The temperature setting switch is “a temperature setting means” for setting a vehicle compartment temperature.

An output side of the microcomputer 100 is connected to the magnetic clutch 30, the fan 70 a of the evaporator 70, the idle adjusting valve 20 c, and the like, via the drive circuits (peripheral circuits) 131 to 133 for driving various actuators. Additionally, the output side of the microcomputer 100 is connected to the electromagnetic volume control valve 10 a of the variable displacement compressor 10. Operations of the various actuators 10 a, 30, 70 a, and 20 c are controlled by output signals from the microcomputer 100.

Next, control processing performed by the microcomputer 100 in the first embodiment is described with reference to flowcharts in FIGS. 2 to 3. In a state where an ignition switch of the vehicle engine (not shown) is turned on, and thereby electrical power is supplied to the microcomputer 100 by a battery B, this control routine starts in response to the operation signal from the operation switch SW.

At step 1 (S1) in FIG. 2, a flag, a timer, and the like are initialized. The flag includes a starting determination flag Tfig (described later) that indicates whether the variable displacement compressor 10 is started a short while ago, and Tflg equals 0 (zero) (Tflg=0) at S1. The timer is built into the microcomputer 100. In the first embodiment, the timer is “an elapsed time measuring means” for measuring an elapsed time T after the variable displacement compressor 10 starts compression.

At step 2 (S2), the operation signal from the air-conditioning operation switch SW and the detection signals of the group of air-conditioning sensors 121 to 125 and the engine tachometer 126 are read.

At step 3 (S3), control states of the various actuators (air-conditioning controllers) 10 a, 30, and 70 a for controlling air conditioning are determined. More specifically, the control signal for the magnetic clutch 30 is determined to energize the magnetic clutch 30. Furthermore, a target outlet temperature TAO is calculated, and a control voltage Vfan applied to an electric motor of the fan 70 a, the control current In of the electromagnetic volume control valve 10 a of the variable displacement compressor 10, and the like are determined based on the target outlet temperature TAO.

The target outlet temperature TAO is calculated based on an air-conditioning heat load fluctuation, the vehicle compartment temperature (inside air temperature) Tr, and a set temperature Tset, which is set by the temperature setting switch of the air-conditioning operation switch SW using the following equation (F1): TAO=Kset×Tset−Kr×Tr−Kam×Tam−Ks×Ts+C  (F1) Tr is the inside air temperature detected by the inside air sensor 122. Tam is the outside air temperature detected by the outside air sensor 121. Ts is the solar radiation amount detected by the solar radiation sensor 123. Kset, Kr, Kam, and Ks are control gains. C is a constant for correction.

At step 4 (S4), the estimated driving torque STrk of the variable displacement compressor 10 is estimated. S4 is described in detail using the flowchart in FIG. 3. At step 41 (S41), it is determined whether the variable displacement compressor 10 is started a short while ago. More specifically, when the starting determination flag Tflg equals 0 (zero) (Tflg=0), it is determined that the variable displacement compressor 10 is started a short while ago, and control proceeds to step 42 (S42). When the starting determination flag Tflg does not equal 0 (zero) (Tflg≠0), it is determined that the variable displacement compressor 10 is not started a short while ago, and control proceeds to step 45 (S45).

At S42, based on the discharge refrigerant pressure Pd (discharge side detection value) and the evaporator outlet air temperature Te (inlet side detection value), which are read at S2, an estimated response time Ter from the time the variable displacement compressor 10 starts compression until compressor driving torque starts increasing is determined.

More specifically, the suction refrigerant pressure Ps of the variable displacement compressor 10 is calculated based on the evaporator outlet air temperature Te, and a high-low pressure ratio (Pd/Ps) of the discharge refrigerant pressure Pd to the suction refrigerant pressure Ps is calculated. Based on the high-low pressure ratio Pd/Ps, the estimated response time Ter is determined by referring to a control map, which is stored in the microcomputer 100 in advance.

In the first embodiment, the map, in which the estimated response time Ter becomes long as the high-low pressure ratio Pd/Ps increases, is employed. Besides, the estimated response time Ter is used for calculating first estimated driving torque as described later.

At step 43 (S43), based on the discharge refrigerant pressure Pd (discharge side detection value) and the evaporator outlet air temperature Te (inlet side detection value), which are read at S2, an increase rate ΔTrkA, at which the first estimated driving torque TrkA is linearly increased as the elapsed time T increases, is determined. More specifically, as in the case of the estimated response time Ter, based on the high-low pressure ratio Pd/Ps, the increase rate ΔTrkA is determined by referring to the control map stored in the microcomputer 100 in advance.

In the first embodiment, the map, in which the increase rate ΔTrkA decreases as the high-low pressure ratio Pd/Ps increases, is employed. At S42, S43, as shown in FIG. 4, an estimated line for the first estimated driving torque TrkA, with the elapsed time T being its variable, is determined. FIG. 4 shows variation of actual driving torque (continuous line) under predetermined conditions, the first estimated driving torque TrkA (dashed line), and second estimated driving torque TrkB (dashed-two dotted line) (described later).

At step 44 (S44), control proceeds to S45 with Tflg being one (Tflg=1). At S45, the first estimated driving torque TrkA is calculated based on the estimated line for the first estimated driving torque TrkA and the elapsed time T. Accordingly, as shown in FIG. 4, the first estimated driving torque TrkA is 0 [N·m] when the elapsed time T is smaller than the estimated response time Ter. The first estimated driving torque TrkA gradual increases according to the increase rate ΔTrkA when the elapsed time T is equal to or larger than the estimated response time Ter.

At step 46 (S46), based on the discharge refrigerant pressure Pd (discharge side detection value), which is read at S2, the second estimated driving torque TrkB is calculated. More specifically, TrkB is calculated using the following equations (F2) to (F4). L=(κ/κ−1)×Psc×Qs×{(Pd/Psc)(κ⁻¹/κ)−1}  (F2) Qs=Vc×Nc×ηv  (F3) TrkB=L/Nc  (F4) The equation (F2) is generally used for calculating power consumption L of a compressor. κ is an adiabatic exponent, Psc is a central value (fixed value) of a pressure on a low-pressure side when the refrigerating cycle is in normal operation, and Qs is a flow rate of vapor-phase refrigerant on the inlet side of the compressor.

The equation (F3) is for calculating Qs. Vc is the discharge volume, Nc is a compressor rotational speed, and ηv is volumetric efficiency of the compressor. Therefore, κ, Psc, and ηv are fixed values. Moreover, Vc is calculated based on the control current In, which is determined at S3, and Nc is calculated by multiplying the engine rotational speed Ne, which is read at S2, by a pulley ratio.

Consequently, at S46, the power consumption L of the compressor is calculated based on the discharge refrigerant pressure Pd using the equations (F2), (F3), and then, the second estimated driving torque TrkB is calculated using the equation (F4). As a result, the second estimated driving torque TrkB depends only upon variation of the discharge refrigerant pressure Pd.

Accordingly, in the first embodiment, S41 to S45 serve as “a first estimated driving torque calculating means” for calculating the first estimated driving torque TrkA of the variable displacement compressor 10 based on the discharge refrigerant pressure Pd and the suction refrigerant pressure Ps. As well, S46 serves as “a second estimated driving torque calculating means” for calculating the second estimated driving torque TrkB of the variable displacement compressor 10 based on the discharge refrigerant pressure Pd.

At step 47 (S47), when TrkA is smaller than TrkB (TrkA<TrkB), control proceeds to step 48 (S48) to set the estimated driving torque STrk at TrkA (STrk=TrkA). When TrkA is not smaller than TrkB, control proceeds to step 49 (S49) to set the estimated driving torque STrk at TrkB (STrk=TrkB). That is, at S47 to S49, a smaller value is chosen between TrkA and TrkB as the estimated driving torque STrk. Then, control proceeds to step 5 (S5) in FIG. 2.

Consequently, in the first embodiment, S47 to S49 serve as “an estimated driving torque determining means” for choosing the smaller value between the first estimated driving torque TrkA and the second estimated driving torque TrkB as the estimated driving torque STrk.

At S5, the driving voltage Visc, which is outputted to the idle adjusting valve 20 c, is determined. The driving voltage Visc is determined such that the engine rotational speed Ne is approximated to a predetermined target idle speed Nco (e.g., 600 to 800 rpm) when the engine is in an idle state.

More specifically, by adding an adding driving voltage Visc2, which corresponds to the estimated driving torque STrk, to a reference driving voltage Visc1, which is determined in advance such that the engine rotational speed Ne coincides with the target idle speed Nco, a driving voltage Vn may be determined.

At step 6 (S6), signals are outputted from the microcomputer 100 to the idle adjusting valve 20 c and the air-conditioning controllers 10 a, 30, and 70 a via the drive circuits 131 to 133 in order to obtain a control state, which is determined at S3, S5. Following standby during a control period τ and it is determined that the control period τ elapses at step 7 (S7). Then, control returns to S2.

In the first embodiment, the estimated driving torque STrk of the variable displacement compressor 10 is estimated by the above control. Based on the estimated driving torque STrk, by controlling the driving voltage Visc, which is outputted from the microcomputer 100 to the idle adjusting valve 20 c, the engine rotational speed Ne in the idle state does not fluctuate even if the driving torque of the compressor changes.

Accordingly, the high-pressure pressure sensor 125, the evaporator temperature sensor 124, the electrical control unit, and S4 in the control routine serve as “a compressor driving torque estimating apparatus”, and the compressor driving torque estimating apparatus, the idle adjusting valve 20 c, the electrical control unit, and S5, S6 in the control routine serve as “a compressor driving source control apparatus”.

Furthermore, in the first embodiment, the first estimated driving torque calculating means (S41 to S45) determine the estimated response time Ter and the increase rate ΔTrkA to calculate the first estimated driving torque TrkA, based on the discharge refrigerant pressure Pd and the evaporator outlet air temperature Te. Thus, as shown in FIG. 4, the first estimated driving torque TrkA is accurate by restricting its difference from the actual compressor driving torque in a transient state immediately after the variable displacement compressor 10 starts compression.

Then, the estimated driving torque determining means (S47 to S49) choose the smaller value between the first estimated driving torque TrkA and the second estimated driving torque TrkB as the estimated driving torque STrk. Therefore, the first estimated driving torque TrkA is chosen in the transient state immediately after the starting of the compression. After the refrigerating cycle Rc is stabilized, the second estimated driving torque TrkB, which is calculated using the equations (F2) to (F4), is chosen.

In the first embodiment, even in the transient state immediately after the variable displacement compressor 10 starts compression, the idle speed is controlled based on the estimated driving torque STrk, which is accurate with its difference from the actual driving torque limited. As a result, stability of the idle speed can be considerably improved.

Second Embodiment

In the first embodiment, the discharge refrigerant pressure Pd is used as the discharge side detection value. In a second embodiment of the present invention, the control current In of the electromagnetic volume control valve 10 a of the variable displacement compressor 10 is used as the discharge side detection value. In addition, the other configurations are the same as the first embodiment.

FIG. 5 is a graph showing a relationship between the discharge refrigerant pressure Pd and the control current In with its horizontal axis being the control current In, and its vertical axis being the discharge refrigerant pressure Pd. Results of a survey, in which a refrigerant discharge flow rate of the variable displacement compressor 10 is changed into a low flow rate, an intermediate flow rate, and a high flow rate, are plotted on the graph. At each flow rate, FIG. 5 shows a correlation between the control current In and the discharge refrigerant pressure Pd.

Thus, even when the control current In of the electromagnetic volume control valve 10 a is used as the discharge side detection value, a similar effect to the first embodiment can be produced. Furthermore, since the control current In is an electrical signal, it can be readily detected.

Other Embodiments

The present invention is not limited to the above embodiments, and various modifications can be made on the present invention as below.

(1) In the above embodiments, the discharge refrigerant pressure Pd and the control current In of the electromagnetic volume control valve 10 a are used as the discharge side detection values. Nevertheless, the discharge side detection value is not limited to these. For example, a compressor rotational speed under predetermined conditions may be used.

Moreover, the discharge refrigerant pressure Pd is not limited to a pressure of refrigerant immediately after it is discharged from the variable displacement compressor 10. Alternatively, a high-pressure side refrigerant pressure in a refrigerant passage from the discharge side of the variable displacement compressor 10 to an inlet side of the expansion valve 60 may be detected for the discharge refrigerant pressure Pd.

(2) In the above embodiments, the evaporator outlet air temperature Te is used as the inlet side detection value. However, the inlet side detection value is not limited to this. For example, temperature of a heat exchanger fin of the expansion valve 60 may be used as the inlet side detection value.

Furthermore, a low-pressure pressure sensor, which detects a pressure of refrigerant drawn into the variable displacement compressor 10 (i.e., refrigerant pressure in the piping P1), may be employed as the inlet side detecting means. Then, the suction refrigerant pressure Ps detected by the low-pressure pressure sensor may be used as the inlet side detection value. Besides, a low-pressure side refrigerant pressure in a refrigerant passage from the outlet side of the expansion valve 60 to the inlet side of the variable displacement compressor 10 may be detected as the suction refrigerant pressure Ps.

(3) In the above embodiments, the estimated driving torque determining means (S47 to S49) choose the smaller value between the first estimated driving torque TrkA and the second estimated driving torque TrkB as the estimated driving torque STrk. Additionally, when the elapsed time T is shorter than a predetermined fiducial time, the first estimated driving torque TrkA may be used as the estimated driving torque STrk in priority to the second estimated driving torque TrkB.

In such a case, regardless of the magnitude of the first estimated driving torque TrkA and the second estimated driving torque TrkB, the first estimated driving torque TrkA is used as the estimated driving torque STrk when the elapsed time T is shorter than the predetermined fiducial time. Thus, the first estimated driving torque TrkA is reliably used as the estimated driving torque STrk in the transient state immediately after the starting of the compression.

(4) In the above embodiments, the estimated response time Ter and the estimated increase rate ΔTrkA are determined based on the high-low pressure ratio Pd/Ps. However, a method of determining the estimated response time Ter and the estimated increase rate ΔTrkA is not limited to this. For example, a plurality of control maps that correspond to a combination between the discharge refrigerant pressure Pd and the suction refrigerant pressure Ps may be stored in the microcomputer 100 in advance. By referring to these control maps, the estimated response time Ter and the increase rate ΔTrkA may be determined.

In the above embodiments, the increase rate ΔTrkA is determined based on the high-low pressure ratio Pd/Ps at the time the variable displacement compressor 10 starts compression. In addition, after the starting of the compression as well, ΔTrkA may be varied sequentially based on the discharge side detection value and the inlet side detection value. By this method, the estimated driving torque STrk can be estimated with a higher degree of accuracy.

(5) In the above embodiments, a predetermined value is used as the reference driving voltage Visc1 for determining the driving voltage Visc of the idle adjusting valve 20 c. Alternatively, based on a deviation En (En=Nco−Ne) (calculated using another control routine) between the engine rotational speed Ne and the target idle speed Nco, the reference driving voltage Visc1 may be determined by a feedback control method using proportional-integral control (PI control) or the like so that the engine rotational speed Ne is approximated to the target idle speed Nco.

Besides, in the control routine of the controlling of the idle speed based on the estimated driving torque STrk in the above embodiments, the above feedback control may be concurrently performed.

(6) In the above embodiments, the electrical control unit includes the microcomputer 100 and its peripheral circuits 110, 131 to 133, and thereby the air-conditioning controllers 10 a, 30, and 70 a are controlled, the estimated driving torque STrk is determined, and the idle adjusting valve 20 c is controlled by the sole electrical control unit. Alternatively, the above control may be performed in communication between a plurality of electrical control units.

For example, in a commonly used vehicle, in which the air-conditioning controllers 10 a, 30, and 70 a are controlled by an air-conditioning control ECU, and the idle adjusting valve 20 c is controlled by an engine ECU, either one of the ECUs may determine the estimated driving torque STrk.

(7) The application of the present invention is not limited to the idle-speed control apparatus. As long as it accords with the purpose of the invention, which is described in claims, the application is not limited to the above embodiments, and the present invention may be applied to a variety of uses.

For example, the present invention may be applied to a stationary heater or cooling apparatus including the variable displacement compressor with a stationary engine being its driving source. Moreover, it may be applied when, in a system that has the variable displacement compressor with an electric motor being its driving source, an amount of electrical power supplied to the motor is controlled based on the estimated driving torque STrk to maintain a regular rotational speed of the electric motor.

Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. 

1. A compressor driving torque estimating apparatus for estimating driving torque of a variable displacement compressor, discharge volume of fluid of which is variable, the apparatus comprising: a discharge side detecting means for detecting discharge side physical quantity about fluid discharged from the variable displacement compressor; an inlet side detecting means for detecting inlet side physical quantity about fluid drawn into the variable displacement compressor; a first estimated driving torque calculating means for calculating first estimated driving torque of the variable displacement compressor based on the discharge side physical quantity and the inlet side physical quantity; a second estimated driving torque calculating means for calculating second estimated driving torque of the variable displacement compressor based on the discharge side physical quantity; and an estimated driving torque determining means for choosing a smaller value between the first estimated driving torque and the second estimated driving torque as the driving torque.
 2. The compressor driving torque estimating apparatus according to claim 1, wherein: the first estimated driving torque calculating means determines an estimated response time from a time when the variable displacement compressor starts compression until the driving torque starts increasing; and the first estimated driving torque calculating means sets the first estimated driving torque at 0 (zero) N·m when an elapsed time from the time when the variable displacement compressor starts the compression is shorter than the estimated response time, and calculates the first estimated driving torque such that the first estimated driving torque increases gradually as the elapsed time increases, when the elapsed time is equal to or longer than the estimated response time.
 3. The compressor driving torque estimating apparatus according to claim 1, wherein: the variable displacement compressor varies the discharge volume based on an external electrical control signal; and the discharge side physical quantity is the control signal.
 4. A compressor driving source control apparatus comprising the compressor driving torque estimating apparatus recited in claim 1, wherein the compressor driving source control apparatus controls an output of a driving source, which provides driving force for the variable displacement compressor, based on the driving torque estimated by the compressor driving torque estimating apparatus.
 5. The compressor driving source control apparatus according to claim 4, wherein: the variable displacement compressor is installed in an air conditioner for a vehicle; and the driving source is an engine of the vehicle.
 6. The compressor driving torque estimating apparatus according to claim 2, wherein the first estimated driving torque calculating means determines the estimated response time based on the discharge side physical quantity and the inlet side physical quantity at the time when the variable displacement compressor starts the compression.
 7. The compressor driving torque estimating apparatus according to claim 2, wherein the first estimated driving torque calculating means determines an increase rate, at which the first estimated driving torque is gradually increased, based on the discharge side physical quantity and the inlet side physical quantity at the time when the variable displacement compressor starts the compression.
 8. The compressor driving torque estimating apparatus according to claim 2, wherein the estimated driving torque determining means chooses the first estimated driving torque as the driving torque in priority to the second estimated driving torque, when the elapsed time is shorter than a predetermined reference time. 